cyclone in this comment describes how Zabbix server processes the fuzzytime() function at the moment. The key moment is: the current value of item is compared with timestamp of this value. As result, it makes useless trigger expressions like "host:system.localtime.fuzzytime(SomeValue)" if this metric is collected by agent in active mode, as value and timestamp should be equal "by design" in this case.

At the same time, documentation always has the following description for trigger function fuzzytime():

Checking how much an item value (as timestamp) differs from the Zabbix server time.

Key moment: "differs from the Zabbix server time" but anything else (including value's timestamp)!

I believe that the behaviour of this trigger function should be modified according to documentation. In result, we could use this metric by active-mode agents, too.

I understand that it could cause to some problems (for example, false positives if some values have been buffered and delayed by active-mode agents and intermediate proxies), but these problems much more predictable and understandable than the current behaviour. The possibility to monitor time deviation using the standard active-mode agent is another very important reason.